Tribute to the great Greek astrophysicist. The scientific world lost a great man last August, Dionysis P. Simopoulos. The distinguished astrophysicist lost his battle with cancer, after first fighting it bravely, with all the positive energy and drive for which he was always distinguished in his life. "Secrets of the Universe" is a series of illustrated books, presenting everything that modern scientists have discovered in recent years, with the help of instruments at their disposal in observatories, accelerators, observatories and spacecraft, about the various wonders that comprise the universe. Because the universe, and everything it contains, is full of secrets that are hidden in the bright paths of colorful stars and strange planets. Nevertheless, with each new generation nature lets us see deeper and deeper into the mysteries it hides. Because, as Aristotle said 2,300 years ago: "All men are naturally hungry for knowledge", it is in the nature of man to want to learn. And this is what makes us hunters of knowledge, experimenters and explorers, in an effort to discover "The Secrets of the Universe".